The National Airspace System (NAS) provides minimal surface surveillance at small to medium airports. The view of the air traffic controller out the window and voice communication with pilots are the primary means of avoiding conflicts and maintaining operational capacity and safety. If visibility is reduced due to weather conditions, then capacity and safety may be severely restricted without some means of surface surveillance.
To improve safety at small to medium-sized airports, the Federal Aviation Administration Air Traffic Organization (ATO, See, www.ato.faa.gov) Advanced Technology Development and Prototyping Group is proposing a Low Cost Ground Surveillance (LCGS) system be developed and implemented.
This LCGS concept provides scalable and adaptable coverage from user-specified regions to an entire airport movement area. Two different LCGS candidates are under evaluation: the Critical Area Management System (CAMS) and the NOVA 9000 Air Traffic Control System (ATCS). See: http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/operations/td/projects/lcgs/, incorporated herein by reference.
CAMS, from Transtech Airport Solutions, Inc. (http://www.transtech-solutions.com/products/asm/airport.html) uses an array of millimeter wave sensors (MWS) distributed throughout the airport movement area to provide coverage of runways, taxiways, and ramp areas. MWS requires no aircraft-installed equipment to operate. The current system installed at Spokane International Airport (GEG), as part of the LCGS evaluation, is integrated with ARTS-IIE. This system can also be integrated with an Optical Identification Sensor (OIS) currently under evaluation.
The NOVA 9000 Air Traffic Control System (ATCS) from Park Air Systems of Horten, Norway, uses Terma X-Band radar to provide complete coverage of the airport movement area. It requires no aircraft-installed equipment to operate. The current system installed at GEG is also integrated with ARTS-IIE.
Both the CAMS and NOVA systems do not require the use of special equipment in the aircraft, making them well-suited for smaller airport use, where aircraft may only have simple radios and transponders. However, both systems rely upon radars and radar type devices, which may be prone to shading and dead spots in coverage. Moreover, such radar transmitters may be expensive to install, and may require FCC approval and/or may interfere with other radars and radio signals. In addition, while such systems may be able to track aircraft and objects, if they cannot read transponder data from aircraft, they cannot identify aircraft individually (e.g., by registration or flight number)
Evers, U.S. Pat. No. 6,211,811, issued Apr. 3, 2001, and incorporated herein by reference, discloses a method and apparatus for improving the surveillance coverage and target identification in a radar based surveillance system. The Evers '811 patent is assigned to the same assignee as the present application and names an inventor in common.
The surveillance of the Evers '811 patent provides a means to measure Time Difference of Arrival (TDOA) and decode identification of signal source transmissions. TDOA and identification information received from a minimum of two receiving means is used to supplement non-cooperative surveillance systems (e.g., primary radar, acoustic sensors) with target identification. The system uses a Line Of Position technique to determine position. The system can be implemented as a standalone multilateration surveillance system, which provides signal source position determination when reception is available from a minimum of two receiving means. The system provides position aiding when implemented to supplement non-cooperative surveillance systems.
Standalone multilateration systems do not require the use of radio transmitters or radar transmitters in order to track aircraft and other vehicles. Rather, using a plurality of radio receivers, it is possible to track aircraft using aircraft signals ordinarily generated from the aircraft—e.g., transponder signals, radio signals, and the like. From these signals, one can track the position of the aircraft and identify the aircraft as well. However, for smaller aircraft, such transponder signals may only be generated in response to an interrogation signal from a conventional ATC radar. A passive multilateration system may not interrogate aircraft transponders to generate aircraft signal data.
Multilateration systems may also be used in conjunction with radar systems to provide redundant tracking data, to confirm radar data and serve as backup if radar should fail or a vehicle or aircraft is in an area of no radar coverage. In addition, data from a multilateration system may be fused with radar data to provide an enhanced data stream of robust and redundant tracking and identification data.
Different types of data signals may be generated by aircraft for various tracking and collision avoidance systems. The Mode S Transponder has the ability to utilize many different formats to communicate air-to-air and air-to-ground. These formats are separated into “short” messages (56 bits long) and “long” messages (112 bits long). A “UF” message is from the interrogator (can be a ground station or a TCAS—Traffic Collision Avoidance System) to the Mode S transponder.
Level 1 is the minimum Mode S Transponder. It has the ability to reply to Mode S interrogations, but it does not have any datalink capability. The message formats used by a Level 1 transponder are all short (56 bit) messages and may include UF messages, which are interrogations to the Transponder. UF messages may include: UF 0—Short Special Surveillance; UF 4—Surveillance, Altitude Request; UF 5—Surveillance, Identity Request; and UF 11—Mode S Only All Call. A “DF” message is a reply from the Mode S transponder to the interrogator, and may include: DF 0—Short Special Surveillance; DF 4—Surveillance, Altitude Reply; DF-5 Surveillance, Identity Reply; and DF 11—All Call Reply.
Rannoch Corporation, predecessor to ERA Systems, Inc, assignee of the present invention, worked with NASA on a Small Business Innovation Research project, proposal number 98-1 01.02-9780B entitled “Low-cost Aircraft Identification and Surveillance System” incorporated herein by reference.
That system provided a low-cost (i.e., under $300K) 1090 MHz Multilateration/Line of Position (LOP)/Automatic Dependent Surveillance-Broadcast (ADS-B) surface surveillance system, which uses the following cost-saving technology innovations: a two-receiver identification/position determination algorithm, GPS synchronization, and passive Mode A/C multilateration. The system addressed FAA Topic 01 Aviation Safety & Capacity, Subtopic 01.02 Advanced Concepts in Air Traffic Management, by providing low-cost surveillance technology, which can be used to locate and identify traffic operating on the airport surface. This surveillance enhances safety by enabling Air Traffic Control (ATC) to have a situational display of traffic movement, as well as automatic runway incursion detection alerting. The system may be used as an enhancement to primary surface radar (i.e., Airport Surface Detection Equipment or ASDE-3) by providing identification of aircraft targets and providing surveillance position aiding in regions where the radar does not provide reliable coverage. Another application of the system is standalone aircraft surveillance; a low-cost standalone system is needed at airports that have not qualified for any currently fielded surveillance system due to cost-benefits ratio analyses.
The multilateration/LOP/ADS-B surface surveillance system has a number of commercial applications: (1) Airport surface surveillance to support runway incursion detection; (2) Airport surface surveillance to support traffic automation for FAA systems such as Surface Movement Advisor; (3) Airport surface surveillance to support NASA's Dynamic Runway Occupancy Monitoring system; (4) Terminal area surveillance to support Precision Runway Monitoring; and (5) Terminal area surveillance to provide surveillance of ADS-B-equipped aircraft.